Embodiments described herein generally relate to oscillators for integrated circuits, and more particularly, embodiments described herein relate to a detector for detecting a type of oscillator used with an integrated circuit.
Unless otherwise indicated herein, the circuits and circuit method described in the background section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in the background section.
Integrated circuits (ICs) are often configured to operate under the control of a clock signal. An external-clock signal may be provided to an IC by an external oscillator, which is external to the IC. Alternatively, an internal-clock signal may be generated by an internal oscillator, which is internal to the IC. An engineer considering the use of an IC will often determine whether an external oscillator or an internal oscillator is to be used for an IC.
FIG. 1A is simplified circuit schematic of an IC 100 configured for use with an external oscillator 105. FIG. 1B is a simplified schematic of IC 100 configured for use with an internal oscillator 110. IC 100 may be on a chip and may include three bond pads 115a, 115b, and 115c to configure the IC for use with an external oscillator or an internal oscillator. The first bond pad 115a is referred to as the crystal-in pad and is labeled XTAL_IN in FIGS. 1A and 1B. The second bond pad 115b is referred to as the crystal-out pad and is labeled XTAL_OUT in FIGS. 1A and 1B. The third bond pad 115c is referred to as the external-internal select pad.
If the external oscillator is configured to supply an external-clock signal to IC 100, the external oscillator is coupled to the crystal-in pad, which is configured to receive the external-clock signal from the external oscillator. The external oscillator is often external to the IC package, which houses the IC. If the external oscillator is configured to provide the external-clock signal to the IC, then the internal oscillator is configured to be turned off and not generate the internal-clock signal. The external-internal select bond pad is typically coupled to a power source Vdd to indicate to the IC that an external oscillator is to supply the external-clock signal to the IC.
If an external oscillator is not configured to supply the external-clock signal the IC, then the internal oscillator is configured to generate the internal-clock signal. For the internal oscillator to generate the internal-clock signal, a crystal oscillator 120 is coupled to both the clock-in pad and the clock-out pad. The crystal oscillator is configured to provide a reference-clock signal to the internal oscillator for generating the internal-clock signal. The external-internal bond pad is typically coupled to ground to indicate to the IC that the internal oscillator is to generate the internal-clock signal.
The external-internal bond pad may be tied to Vdd or ground within the IC package in which the IC is housed. For example, a bond wire or the like may be coupled to the Vdd plane or ground plane of a lead frame of the IC package. Customers who purchase ICs, which have the option of coupling to an external clock or operating an internal clock, will specify to an IC seller whether the customer intends to use the IC with an external clock or an internal clock so that an IC with the external-internal bond pad appropriately tied to Vdd or ground is sold to the customer. IC manufacturers must therefore have two IC packaging options for such ICs, which tends to drive up the cost of designing and producing such ICs.
New ICs are needed that provide alternative options for determining within the ICs whether an external oscillator or an internal oscillator is configured to generate a clock signal for the IC.